There are a three of waiting periods:
1) Time from submitting applications to getting provisional clearance (which allows you to book your interview). When I did my renewal this summer, this took about three months. I thought mine was long because it was a bit complicated - since getting my NEXUS, I've lived in three countries (two continents), had (and then dropped) US residency status, had two US G4 (diplomatic) visas, got a UN Laissez Passer (essentially a passport-like thing that people who work for international organizations can travel on, and had something like 24 countries in my list of countries visited (including a few that raised eyebrows, or at least questions from the US agent at the interview). However, my aunt and uncle with very simple renewal took about the same time.
Looking at Flyertalk, it looks to be about 2 months right now (
https://www.flyertalk.com/forum/tru...me-applications-processing-timelines-115.html).
Also, note that they don't send you an email that this has come through (at least they don't for the renewal), you have to just keep checking your account.
2) Time from getting provisional clearance to getting interview. This can vary greatly. Depends on how many of you there are and the location you want (as Bumbershoot says, different places have different availability). If you can only book far out, keep checking for cancellations, I was able to snack an appointment at Pearson Airport (a busy one) a few days after getting my notice because there was a cancellation.
3) Time from interview to getting your card. This took about 10 days for my renewal. It's pretty quick.
Honestly, I think most of my original interview was more about ways I could mess up and get my status revoked! Just make sure that you bring everything that they tell you to bring - including printing out the letter inviting you to the interview. Since you're a US resident you need to bring proof of your address (same with Canadian residents - for international residents, they don't require proof of address).
For making sure it is on your boarding pass. Make sure that your name on your ticket exactly matches that on your pass (e.g. if you have a middle name on the pass, make sure to include your middle name on your ticket). Most airlines let you put your KTN on your profile. Do so. If you don't have a profile (or it doesn't work), you can add it during your check-in process.